A polymer molded product with a fine structure has been increasingly utilized in various fields such as electronic devices, optical devices, recording media, and medical/bio device. Various methods for manufacturing such a molded product with fine structure have been proposed but attention has been attracted to a UV and thermal nanoimprint method owing to high economic efficiency and productivity. Of nanoimprint methods, there is a hot embossing (thermal nanoimprint) method in which a stamper mold is pressed to a polymer substrate softened under heating to cause plastic deformation, thereby transfer-molding a pattern of the stamper mold. The hot embossing method has a high productivity and has advantages such as capability of fabrication of fine patterns of various thermoplastic polymer substrates.
However, the hot embossing (thermal nanoimprint) method has a problem that, in the filling stage of a fine structure of a high aspect ratio, fluidity of a polymer is insufficient or high pressure is needed. Also, the hot embossing method has a problem that, when the polymer is heated to the melting temperature, the fluidity of the polymer exceedingly increases and the polymer substrate only undergoes deformation of extending in a plane direction even when pressed, and thus the polymer is not filled into a deep groove portion of the fine structure at which flow resistance is large. For the problem, for example, PTL 1 proposes a method of manufacturing a molded product with a nano-structure and a micro-structure, which includes a step of placing a powdery polymer on the surface of an original plate, a step of heating the original plate and the polymer to a temperature equal to or higher than the glass transition temperature of the polymer and equal to or lower than the melting temperature, a step of pressing the polymer to the original plate, and a step of removing the original plate after cooling the polymer to a temperature equal to or lower than the glass transition temperature so as to form a reverse structure of the nano-structure and the micro-structure of the original plate.
On the other hand, besides the above-described hot embossing method, there is a UV optical nanoimprint method in which, after a liquid photo-curable polymer is coated on a substrate at room temperature, an optically transparent stamper mold is pressed to the polymer, the polymer is irradiated with a light through the stamper mold to cure the polymer, thereby transcribing a pattern onto the polymer substrate. The UV optical nanoimprint method has advantages that processing can be performed at room temperature, transcribed pressure is low, and a highly accurate pattern can be molded.
However, in the UV optical nanoimprint method, although the pressure for transcription is low, a photo-curable polymer generally exhibits small shrinkage at curing and has properties resemble to an adhesive, so that it is difficult to release the imprinted film polymer from the stamper mold and thus there is a concern that a fine structure of the stamper mold is broken through releasing the imprinted film. For the problem, PTL 2 proposes a manufacture method in which a replica is formed based on a stamper mold original plate and use the replica as a stamper mold in the UV optical nanoimprint step. Namely, PTL 2 proposes a method for manufacturing a polymer-made imprinted film with fine structure having a minimum processing size of 1,000 nm or less, which includes a step of forming a coating film on the surface of a fine structure having a fine concavo-convex pattern of 1,000 nm or less and being composed of a polymer formed by polymerization, a step of pressing the imprinted film with fine structure to a polymer precursor monomer or a composition of a polymer precursor monomer and polymerizing the polymer precursor monomer or the composition of a polymer precursor monomer, and a step of releasing the imprinted film with fine structure from the polymer of the polymer precursor monomer or the composition of a polymer precursor monomer to transfer the fine concavo-convex pattern on the surface of the imprinted film with fine patterns to the polymer.
Further, the UV nanoimprint method is a method of coating an adhesive composed of a UV photo-curable polymer after coating a stamper mold with a polymer, pressing a transparent stamper mold thereto and irradiating it with an ultraviolet ray to cure the adhesive, and subsequently releasing the polymer together with the transparent stamper mold from the stamper mold to thereby stamp a imprinted film with fine pattern. Therefore, the method has problems that the number of steps is large and thus the production costs increase. For this problem, PTL 3 proposes a method for transferring a fine structure, which includes a step of coating a solvent on a surface of a stamper mold having a fine structure, a step of bringing a polymer substrate into contact with the solvent on the stamper mold, and a step of releasing the stamper mold from the polymer substrate.
PTL 4 proposes a method for transcribing a molded fine structure not by heating and softening a polymer substrate but using a molten polymer. Namely, PTL 4 proposes a method for manufacturing a molded product, which includes coating a molten polymer on a stamper mold having fine concavity and convexity, pressing it, and subsequently cooling and solidifying it to obtain a molded product having a fine concavo-convex transfer-molded thereto, wherein the feed of the molten polymer onto the stamper mold having the fine concavo-convex pattern on its surface is performed so that the shape and thickness are almost close to those of a final molded product with moving a molten polymer discharge port and the moltenc polymer is attached to the inside of the fine concavo-convex pattern. According to the method for manufacturing a molded product, it is said that a molded product where the shape of the fine concavo-convex pattern has a width or diameter of 10 nm to 1 mm and a depth or height of 10 nm to 1 mm can be manufactured.
PTL 5 proposes a method of coating a thermoplastic polymer using a T die on a surface to be coated having a fine pattern in a predetermined thickness with relatively moving the surface to be coated and the discharge port, and subsequently and immediately pressing the coated polymer with a pressurizing roller with maintaining a condition that attaching force between the polymer and the pressurizing roller is lower than attaching force between the polymer and a mold, so as to accelerate the filling of the polymer coated on the surface to be coated into the fine pattern and also achieve flatness of the thickness of the coated polymer and transcription of a mirror surface to the upper surface.